Most electrophotographic copier machines utilize optical components such as lenses and mirrors to direct an image of an original document to an image-receiving, electrostatically-charged surface. Many copier machines then utilize a powdery substance called toner to develop an electrostatic image of the original. Unfortunately, the black powdery toner material is difficult to control and can escape from the photoreceptive surface into the body of the machine itself. Once in the body of the machine the toner can find itself deposited upon the lenses and mirrors of the optical system. When that happens the ability of the optical elements to transmit light is reduced and consequently the images of the original become less sharp over a period of time. Compounding the problem is the fact that toner is a thermoplastic material which when heated adheres to the surface upon which it is deposited. Since significant amounts of heat are produced within the body of a copier machine, the optical elements can become quite hot with the result that toner can be fused to the surface of the optical elements, causing decreased transmission of illumination and increased background on finished copy. To prevent the accumulation of heat on optical components, it is customary to provide a cooling fan to blow ambient air over these components.
U.S. Pat. No. 4,120,578; incorporated herein by reference, discloses an optical system which is relatively free from contamination since all of the optical components are located in an enclosed optical box. While not illustrated in that patent, the system also contains a fan to cool the optical elements. It may be observed that the optical box is not completely closed since a small aperture is located in one side of the optics box to allow the illumination to pass from the optical system onto a moving photoreceptive surface. As a consequence of that opening in the optics box and even though the optics box is somewhat pressurized by the cooling fan, toner powder still manages to enter the optical box through the aperture and contaminate the optical system. Entrance of the toner into the optical box through the aperture is promoted by a pumping action created by the movement of an optical scanning mechanism within the optical box. That movement tends to set up air currents within the box which pumps air through the aperture and toner contamination with it.
It is, therefore, an object of this invention to provide means for channeling air from a cooling fan to the aperture of an optics module so that the air forms a barrier to contaminants otherwise entering the module through the aperture.
Further, it is an object to channel the air without utilizing ductwork which would usurp space needed for machine conponents and interrupt the optical path.